[wasm] Compute memory size instead of hard-coding it

With C++14, we can make {ElementSizeLog2Of} constexpr and use it to
compute the loaded or stored memory size instead of duplicating that
information.

The code does not get shorter this way, but more robust.

R=ahaas@chromium.org

Bug: v8:9810
Change-Id: Idb7e861f833798e181694cda0db21ef57804d3a2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1914215Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64948}

src/codegen/machine-type.h

@@ -53,9 +53,10 @@ enum class MachineSemantic : uint8_t {
   kAny
 };
 
-V8_EXPORT_PRIVATE inline int ElementSizeLog2Of(MachineRepresentation rep);
+V8_EXPORT_PRIVATE inline constexpr int ElementSizeLog2Of(MachineRepresentation);
 
-V8_EXPORT_PRIVATE inline int ElementSizeInBytes(MachineRepresentation rep);
+V8_EXPORT_PRIVATE inline constexpr int ElementSizeInBytes(
+    MachineRepresentation);
 
 class MachineType {
  public:
@@ -322,7 +323,8 @@ inline bool IsAnyCompressed(MachineRepresentation rep) {
 }
 
 // Gets the log2 of the element size in bytes of the machine type.
-V8_EXPORT_PRIVATE inline int ElementSizeLog2Of(MachineRepresentation rep) {
+V8_EXPORT_PRIVATE inline constexpr int ElementSizeLog2Of(
+    MachineRepresentation rep) {
   switch (rep) {
     case MachineRepresentation::kBit:
     case MachineRepresentation::kWord8:
@@ -344,12 +346,17 @@ V8_EXPORT_PRIVATE inline int ElementSizeLog2Of(MachineRepresentation rep) {
     case MachineRepresentation::kCompressed:
       return kTaggedSizeLog2;
     default:
-      break;
-  }
+#if V8_HAS_CXX14_CONSTEXPR
       UNREACHABLE();
+#else
+      // Return something for older compilers.
+      return -1;
+#endif
+  }
 }
 
-V8_EXPORT_PRIVATE inline int ElementSizeInBytes(MachineRepresentation rep) {
+V8_EXPORT_PRIVATE inline constexpr int ElementSizeInBytes(
+    MachineRepresentation rep) {
   return 1 << ElementSizeLog2Of(rep);
 }
 

src/wasm/value-type.h

@@ -54,24 +54,22 @@ using FunctionSig = Signature<ValueType>;
 
 inline size_t hash_value(ValueType type) { return static_cast<size_t>(type); }
 
-// TODO(clemensb): Compute memtype and size from ValueType once we have c++14
-// constexpr support.
 #define FOREACH_LOAD_TYPE(V) \
-  V(I32, , Int32, 2)         \
-  V(I32, 8S, Int8, 0)        \
-  V(I32, 8U, Uint8, 0)       \
-  V(I32, 16S, Int16, 1)      \
-  V(I32, 16U, Uint16, 1)     \
-  V(I64, , Int64, 3)         \
-  V(I64, 8S, Int8, 0)        \
-  V(I64, 8U, Uint8, 0)       \
-  V(I64, 16S, Int16, 1)      \
-  V(I64, 16U, Uint16, 1)     \
-  V(I64, 32S, Int32, 2)      \
-  V(I64, 32U, Uint32, 2)     \
-  V(F32, , Float32, 2)       \
-  V(F64, , Float64, 3)       \
-  V(S128, , Simd128, 4)
+  V(I32, , Int32)            \
+  V(I32, 8S, Int8)           \
+  V(I32, 8U, Uint8)          \
+  V(I32, 16S, Int16)         \
+  V(I32, 16U, Uint16)        \
+  V(I64, , Int64)            \
+  V(I64, 8S, Int8)           \
+  V(I64, 8U, Uint8)          \
+  V(I64, 16S, Int16)         \
+  V(I64, 16U, Uint16)        \
+  V(I64, 32S, Int32)         \
+  V(I64, 32U, Uint32)        \
+  V(F32, , Float32)          \
+  V(F64, , Float64)          \
+  V(S128, , Simd128)
 
 class LoadType {
  public:
@@ -110,7 +108,8 @@ class LoadType {
   const LoadTypeValue val_;
 
   static constexpr uint8_t kLoadSizeLog2[] = {
-#define LOAD_SIZE(_, __, ___, size) size,
+#define LOAD_SIZE(_, __, memtype) \
+  ElementSizeLog2Of(MachineType::memtype().representation()),
       FOREACH_LOAD_TYPE(LOAD_SIZE)
 #undef LOAD_SIZE
   };
@@ -122,23 +121,23 @@ class LoadType {
   };
 
   static constexpr MachineType kMemType[] = {
-#define MEMTYPE(_, __, memtype, ___) MachineType::memtype(),
+#define MEMTYPE(_, __, memtype) MachineType::memtype(),
       FOREACH_LOAD_TYPE(MEMTYPE)
 #undef MEMTYPE
   };
 };
 
 #define FOREACH_STORE_TYPE(V) \
-  V(I32, , Word32, 2)         \
-  V(I32, 8, Word8, 0)         \
-  V(I32, 16, Word16, 1)       \
-  V(I64, , Word64, 3)         \
-  V(I64, 8, Word8, 0)         \
-  V(I64, 16, Word16, 1)       \
-  V(I64, 32, Word32, 2)       \
-  V(F32, , Float32, 2)        \
-  V(F64, , Float64, 3)        \
-  V(S128, , Simd128, 4)
+  V(I32, , Word32)            \
+  V(I32, 8, Word8)            \
+  V(I32, 16, Word16)          \
+  V(I64, , Word64)            \
+  V(I64, 8, Word8)            \
+  V(I64, 16, Word16)          \
+  V(I64, 32, Word32)          \
+  V(F32, , Float32)           \
+  V(F64, , Float64)           \
+  V(S128, , Simd128)
 
 class StoreType {
  public:
@@ -177,7 +176,8 @@ class StoreType {
   const StoreTypeValue val_;
 
   static constexpr uint8_t kStoreSizeLog2[] = {
-#define STORE_SIZE(_, __, ___, size) size,
+#define STORE_SIZE(_, __, memrep) \
+  ElementSizeLog2Of(MachineRepresentation::k##memrep),
       FOREACH_STORE_TYPE(STORE_SIZE)
 #undef STORE_SIZE
   };
@@ -189,7 +189,7 @@ class StoreType {
   };
 
   static constexpr MachineRepresentation kMemRep[] = {
-#define MEMREP(_, __, memrep, ___) MachineRepresentation::k##memrep,
+#define MEMREP(_, __, memrep) MachineRepresentation::k##memrep,
       FOREACH_STORE_TYPE(MEMREP)
 #undef MEMREP
   };